Early Diagnosis of Carpal Tunnel Syndrome:
Comparison of Digit 1 with Wrist and Distoproximal Ratio
by Khema R. Sharma, MD, Francisco Rotta, MD, Jose Romano, MD, and D. Ram
Ayyar, MD
Published: 29 March 2001
Our objective in this study was to compare the sensitivity and specificity
of the median sensory nerve conduction velocity (SNCV) from digit 1 to wrist
with those of the distoproximal (D/P) ratio of the median SNCV from palm to
digit 3/palm to wrist in the diagnosis of mild carpal tunnel syndrome (CTS)
by using a receiver operating characteristic (ROC) curve. To achieve this objective,
we studied prospectively (January 1997–October 1998) 370 patients referred
for CTS. One hundred forty-two patients (38.4%) with moderate to severe CTS
and 15 patients (4.1%) with multiple (
3) compressive neuropathies in upper
limbs with subclinical peripheral neuropathy were excluded. The remaining 213
patients (302 hands with mild CTS; 167 women; mean age, 50 y ± 12 y)
and 38 controls (71 hands; 25 women; mean age, 47 y ± 13 y) had median
and ulnar nerve conduction studies. ROC curves were constructed for median SNCV
digit 1 to wrist and median SNCV D/P ratio from the patients' and controls'
data. The median SNCV at 
45.9 m/s, corresponding to an optimal cutoff point
on ROC curve, discriminated 89.5% of mild CTS from controls with specificity
of 98.6%. The median D/P ratio at 1.12, corresponding to an optimal cutoff
point on ROC curve, discriminated 67.2% of mild CTS from controls with specificity
of 97.2%. Of the 10.3% (31/302) of hands in which digit 1 to wrist was within
normal limits at the selected optimal cutoff value (45.9 ms), 7% (21/302)
had an abnormal D/P ratio (1.12), and 3.3% (10/302) had a normal electrophysiologic
examination. The likelihood ratio (true-positive ratio to false-positive ratio,
assessing the discriminative power of a test) of the median SNCV digit 1 to
wrist, at an optimal point on ROC curve (63.9), was higher than that of the
median SNCV D/P ratio (23.9, X2 = 36.9, P < .001). These findings
suggest that the median SNCV digit 1 to wrist is more sensitive than the median
SNCV D/P ratio in the diagnosis of mild CTS.
Keywords: carpal tunnel syndrome, early diagnosis, median sensory nerve
conduction velocity, digit one, distoproximal ratio, receiver operating characteristic
curve, sensitivity, and specificity
Early
Diagnosis of Carpal Tunnel Syndrome: Comparison of Digit 1 with Wrist and Distoproximal
Ratio
by Khema R. Sharma, MD, Francisco Rotta, MD, Jose Romano, MD, and D. Ram
Ayyar, MD
